In an automatic assembly line or the like in the automobile industry, a clamping device for clamping a workpiece for a purpose of processing is frequently used. As such a clamping device, there are already-known devices as disclosed in Japanese Patent Application Laid-open No. 2001-105332, Japanese Patent Application Laid-open No. 2001-310225, Japanese Patent Application Laid-open No. 2001-009741, and the like, for example.
In this clamping device, a first clamping arm is rotated and moved to a clamping position and then a large clamping force for clamping is generated. In this case, the first clamping arm is substantially at no load while moving to the clamping position and therefore a large driving force is not required from a driving source. On the other hand, in a stage of generating the clamping force, the large driving force is required from the driving source.
However, in the conventionally-known clamping device, a common driving source is used as a driving source for rotating and moving the first clamping arm to the clamping position and a driving source for generating a final clamping force. Therefore, if performance of the driving source itself is large enough to generate the clamping force, the performance is too large for rotation of the first clamping arm and also a driving system of the first clamping arm is required to have a strength adapted to the performance of the driving source. If a degree of the performance of the driving source is adapted to a rotating force of the first clamping arm on the contrary, it is difficult to generate a required clamping force.